Perborate salts (also sometimes mentioned hereinbelow as “perborate”) are known bleaches. Perborate, when dissolved in water, forms hydrogen peroxide, which in turn delivers oxygen bleaching benefit. Perborate in aqueous laundry detergent compositions has been described. See, for instance, Del Duka et al., U.S. Pat. No. 6,482,786; European patents EP0080748, EP0181041; Biscarini, U.S. Pat. No. 5,922,083; Showell et al., U.S. Pat. No. 5,419,847 and Boskamp, U.S. Pat. No. 4,526,709. Sanderson et al., U.S. Pat. No. 5,458,802 describes non-aqueous formulations containing perborate for laundry use. EP 0717102 describes a liquid automatic dishwashing detergent containing, among other ingredients, perborate and polyol, the free moisture content of the composition said to be kept at the minimum. Smigel (U.S. Pat. Nos. 4,603,045 and 4,690,776) describes toothpastes containing water, perborate, and polyol.
Some of the disclosures cited above also mention polyol or mixtures of polyol with boric acid or borate salts, which are known enzyme stabilization systems. Mixtures of polyol with boric acid or borates protect the enzyme in the composition by the so called “pH jump” mechanism. See also Panandiker et al., U.S. Pat. No. 5,468,414; Aronson et al., U.S. Pat. No. 5,089,163; Aronson et al., U.S. Pat. No. 4,959,179; Falk et al., U.S. Pat. No. 5,719,117; and Falk et al., U.S. Pat. No. 5,723,434.
A pH jump system functions by adjusting the pH of the wash liquor. To achieve the required pH regimes, a pH jump system is employed to keep the pH of the product low for enzyme stability yet allow it to become moderately high in the wash for detergency efficacy. One such system is borax/polyol complex. Upon dilution, the complex dissociates, liberating free borate to raise the pH. Such borax or boric acid complexes with polyol, however, do not generate perborate bleach and are not bleach systems.
The use of perborate in aqueous compositions has been hampered by the limited solubility of perborate in water, the challenge being to incorporate sufficient amounts of perborate into an aqueous composition to deliver the bleaching benefit and to avoid the presence of undissolved perborate in the composition.